The present invention relates to an ultrasonic wave driven type motor in which a rotor is operated by an ultrasonic vibration to generate a driving force.
Various ultrasonic torsional vibration elements are known in which an annular or disc piezoelectric element is used as a vibrating source for generating a torsional vibration. Such ultrasonic torsional vibration elements are disclosed in Japanese Patent Publication Nos. 3633/76 and 14156/77 and Japanese Patent Kokai Nos. 120677/86 and 120678/86.
For example, Japanese Patent Publication No. 14156/77 discloses a torsional vibrator comprising a plurality of annular or ring-shaped piezoelectric elements each of which is sequentially and partially polarized in the peripheral direction, and the piezoelctric elements are electrically connected in parallel and are mechanically tightened to each other by metal blocks.
Japanese Patent Kokai No. 96882/84 discloses an ultrasonic driven type motor which comprises a stator including a piezoelectric vibrator used as a driving means, and a rotor arranged to be rotatd by the stator. In such a conventional ultrasonic driven type motor, the stator is of an annular shape, to which driving voltage of multiphase is applied for generating a traveling wave, and the rotor is rotated by the generated traveling wave.
With such a conventional ultrasonic driven type motor, however, the control of the applied voltage is complicated, and the generation and adjustment of the driving force are performed only by means of a resonance. Therefore, the conventional motor of the kind mentioned above has disadvantages that it has little adaptability in its design, and the design therefor becomes troublesome.